1. Field of the Invention
The present invention relates to a wind turbine comprising at least one blade adjustment system.
2. Description of the Related Art
In wind turbines of this species, a rotor blade is rotatably affixed with a blade bearing to a rotor hub. The blade adjustment system comprises at least one blade adjustment drive fitted with a drive pinion, a gear unit and an electric or hydraulic drive motor. The drive pinion meshes with the external or inner toothed blade bearing.
Such systems must meet several requirements which can be made technically compatible only with difficulties.
In order to minimize the stresses applied to the adjoining structure, the rotor hub and the blade adjustment system should be both low in weight and economical in manufacture.
On the other hand the blade bearing requires very rigid adjacent connection because warping the connecting flange would shorten bearing life.
Moreover the blade adjustment system should apply in economical manner as large as possible a blade adjusting torque, making it desirable to configure the drive pinion as far outward as possible (long lever arm, away from the blade axis).
Also the blade adjustment system involves a complex drive mechanisms that heretofore preferably was sheltered within the rotor hub.
This problem has been widely addressed by screwing the blade bearing external ring into the rotor hub and by fitting the inner ring with an inner toothing and to link it to the rotor blade. In that case the adjustment drives are situated within the hub. This design suffers from the substantive drawback however that on account of the large flange diameter of the outer bearing ring, the rotor hub must be very heavy and of low rigidity, further that, on account of the smaller lever arm, the adjustment drives can apply only lesser adjustment torques than if an outer toothing were used.
By inverting the blade bearing connection (inner ring screwed to the hub, outer ring to the blade), more compact and therefore more rigid hubs could be made in the state of the art, which thereby however again entailed spatial problems in configuring the blade adjustment drives. The inside of the hub no longer offers adequate space, and, outside the hub, spatial accommodation is restricted so much that as a rule the drives are mounted in a manner that either they point outward relative to the drive pinion (like rotor blades), or the drive pinions are mounted centrally on the side of the hub away from the nacelle (centrally in front of the hub's blade flanges).
In that case, for reasons of space, angle drives are used, that is the axes of rotation of the drive pinion and drive motor subtend an angle larger than 45°, as a rule being 90°. Such a system is described in the German patent document DE 101 41 667. The special configuration however is so packed that access to the rotor hub inside and to the rotor blades required for maintenance must be through so-called blade extenders (tubular components with access apertures). In turn blade extenders entail substantial increases in weight and costs.